Assuming Exchange 2003, go into System Manager, drill down through Admin Groups, First Admin Group, Servers, right-click your server and Properties, Directory Access tab. If Automatically discover servers is checked then all of your DC's should be listed. If not, then either select Automatic or add in your servers for each listing under Show. Also make sure you have moved all of the FSMO roles to one of the new servers, and if this is a single domain both new servers should be Global Catalogs.

Well, to fix this for now you can uncheck Automatically and then manually input your other DC's. Then you can try turning off the old DC and make sure it works. Then you can start looking into the issue why they were not automatically found.

I tried unchecking "Autmatically" and manually inputing the server. Somewhere between that and Microsoft updates I ended up spending last weekend rebuilding the IIS and my exchange front end as all email stopped. As I worked with Microsoft to get email going again, i was strongly advised NOT to uncheck "Automatic discover".

Checked my DNS; Yes the SRV records are in the _tcp folder. (PS. great instructions, DNS is not my strong point and I wasn't sure where to find the SRV records.)

Check your Exchange server IP settings to make sure that you have it pointed to the correct DNS servers. Is everything there on the same subnet? Run the flushdns command to clear the DNS cache on the exchange server. To do that open the command prompt and type ipconfig /flushdns.

If it is only finding one GC, then that is the problem. Any DC that Exchange uses must be a GC or Exchange can't use it. You mentioned earlier that both of the new DC's are GC's - can you confirm that?

Ran the Environment Health Scanner and it didn't come up with anything that I thought would be relevatant. It noticed a differnet subnet, but that subnet has nothing to do with the 3 domain controllers and the exchange controllers. Also notice that a couple of the domain controlers are getting there time from multiple locations.